1. Field of the Invention
The present invention relates to a receiving apparatus and a data rewriting method, and more particularly, is preferably applicable to a digital satellite broadcasting system.
2. Description of the Related Art
A method called Moving Picture Experts Group Phase 2 (MPEG2) has been proposed for coding analog video audio signals and digital video audio data in a television broadcasting system, a High Definition Television (HDTV), an Audio Visual (AV) device, and so on.
The MPEG2 method is provided to encode and then multiplex a predetermined analog signal and digital data. The MPEG2 method recently was used as a method for coding video audio data in accordance with a plurality of programs. As a result, a digital satellite broadcasting system for broadcasting respective programs via a broadcasting satellite toward specified viewers who are allowed to view (who contract as viewers) has been realized to some extent.
The digital satellite broadcasting system has a higher coding efficiency compared to a conventional television broadcasting system for coding video audio signals by the MPEG2 method, so as to realize multichannel broadcasting and to reduce the cost per channel. Thereby, various data for data broadcasting (hereinafter, referred to as service data) can be broadcasted simultaneously in addition to the programs for plural channels, so that the digital satellite broadcasting system will be used increasingly for more purposes.
Such a digital satellite broadcasting system has a plurality of broadcasting forms depending upon the company which manages the system (hereinafter, referred to as a management company). The viewer who is allowed to view programs by contracting with these management companies is required to buy an exclusive digital broadcasting receiver in accordance with the broadcasting form of the corresponding digital satellite broadcasting system.
Accordingly, in a case in which the viewer terminates a contract with a management company and changes a management company to newly contract with another management company (hereinafter, referred to as management company change), the viewer must buy a new digital broadcasting receiver for the new contract, despite that the viewer already owns a digital broadcasting receiver, thereby causing a burden for the viewer.
There are modifiable types of digital broadcasting receivers in addition to the types corresponding to the broadcasting form of the digital satellite broadcasting system. Each of the modifiable types of digital broadcasting receivers stores program data in accordance with the type and the broadcasting form of the corresponding digital satellite broadcasting system in a flash Read Only Memory (ROM) provided inside, and receives programs broadcasted by the corresponding digital satellite broadcasting system based on the program data.
In a case where a viewer changes a management company, the viewer rewrites the program data recorded in the internal flash ROM in his/her own digital broadcasting receiver with the program data in accordance with the broadcasting form of the digital satellite broadcasting system managed by the management company newly contracted and in accordance with the type, so as to use the same digital broadcasting receiver after contract with a new management company.
To actually rewrite the program data of the digital broadcasting receiver, as shown in FIG. 1, when a viewer demands a management company change of a management company which will be newly contracted, in a transmitting apparatus 2 of a digital satellite broadcasting system 1 which is managed by the management company, a data supplying part 3 supplies new program data Dl which is necessary to rewrite (hereinafter, referred to as download data) in accordance with the type of digital broadcasting receiver 4 which is presently owned by the viewer and in accordance with the broadcasting form of the digital satellite broadcasting system 1 to a data transmitting part 6 through a data outputting part 5 during a predetermined fixed period of time repeatedly. At the same time, the data transmitting part 6 modulates the download data D1 by a predetermined method to generate transmission data D2, which is broadcasted toward a broadcasting satellite 8 via an antenna 7.
Then, the transmission data D2 is received by the digital broadcasting receiver 4 of a receiving apparatus 9 which is owned by the viewer via an antenna 10. The digital broadcasting receiver 4 demodulates the transmission data D2 by a predetermined method, and overwrites the flash ROM (not shown) with the obtained download data D1 to rewrite the program data which has been recorded in the flash ROM with the download data D1. Such a method is known.
If the viewer rewrites the program data in this way at the time of the contract with a new management company, the viewer can receive programs from the digital satellite broadcasting system 1 managed by this management company, and can view the received programs through a monitor 11.
However, this method has a problem. While the transmission data D2 is being transmitted from the transmitting apparatus 2, if false transmission data (hereinafter, referred to as false transmission data) containing false download data which has altered contents and contains a virus (hereinafter, referred to as false download data) is transmitted from another transmitting apparatus toward the broadcasting satellite 8 intentionally, the digital broadcasting receiver 4 may receive the false transmission data instead of the transmission data D2 transmitted normally and the false download data obtained based on the false transmission data may overwrite the flash ROM. In this case, the digital broadcasting receiver 4 operates incorrectly based on the false download data.